Where does Ubuntu look for shared libraries?

This whole path business is related to something called multi-arch. Basically it's to allow you to have 32bit and 64bit libraries on the same system.

After you copied the file, did you happen to run ldconfig?

ldconfig  creates,  updates,  and removes the necessary links and cache
       (for use by the run-time linker,  ld.so)  to  the  most  recent  shared
       libraries  found  in  the directories specified on the command line, in
       the file /etc/ld.so.conf, and in the trusted directories (/usr/lib  and
       /lib).   ldconfig  checks the header and file names of the libraries it
       encounters when determining which  versions  should  have  their  links
       updated.  ldconfig ignores symbolic links when scanning for libraries.

The information contained in the above question AND first (and only ATT) answer, helped me resolve *a similar * issue of mine on WSL Ubuntu (on Win10 64)!

In my case the executable couldn't find a library. I ultimately noticed that the newly-made library got positioned in /usr/lib64 , but the multi-arch lines of /etc/ld.so.conf.d/x86_64-linux-gnu.conf did not include that directory.

So I ran

sudo ldconfig /usr/lib64

and that finally fixed it. (running it alone without the directory parameter did not make it 'magically' find the libraries BTW.) It's unclear whether 'restarting' my WSL bash helped... I think that wasn't even needed.